Code style: Change namespace, Use PSR 2, PSR4 and WordPress coding standard

[tangrufus]

No description provided.

[codecov]

Codecov Report

Merging #61 into master will increase coverage by 0.56%.
The diff coverage is 47.61%.

@@             Coverage Diff              @@
##             master      #61      +/-   ##
============================================
+ Coverage     47.05%   47.61%   +0.56%     
- Complexity       61       63       +2     
============================================
  Files            13       13              
  Lines           187      189       +2     
============================================
+ Hits             88       90       +2     
  Misses           99       99

Impacted Files	Coverage Δ	Complexity Δ
src/FunctionInvokerTrait.php	0% <0%> (ø)	6 <6> (?)
src/Settings.php	0% <0%> (ø)	5 <5> (?)
src/FieldConfig.php	0% <0%> (ø)	1 <1> (?)
src/ViewFactory.php	100% <100%> (ø)	2 <2> (?)
src/ViewEchoTrait.php	100% <100%> (ø)	3 <3> (?)
src/OptionStore.php	100% <100%> (ø)	2 <2> (?)
src/Sanitizer.php	100% <100%> (ø)	4 <4> (?)
src/MenuPageConfig.php	100% <100%> (ø)	4 <4> (?)
src/SectionConfig.php	18.75% <18.75%> (ø)	7 <7> (?)
src/MenuPages.php	25% <25%> (ø)	6 <6> (?)
... and 16 more

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